Extrusion of sheathing from aluminum and the like



Oct. 16, 1956 c. c. CHILDRESS 2,766,519

EXTRUSION 0F SHEATHING FROM ALUMINUM AND THE LIKE Filed Feb. 7 1952 INVENTOR CLIFFORD C. Cr-uwasss ATTO RN E nited States EXTRUSION F SHEATHING FROM ALUMINUM AND Tm Lllfli,

This invention relates to the fabrication of aluminum by extrusion. It has particular reference to an improved process by which aluminum can be extruded continuously.

Machines for the continuous extrusion of metals are well known in the art. For example, a screw type of continuous extruder is used for extruding lead to form cable sheathing or tubing. The metal is fed in molten condition to the extiuder, where it is conveyed by a rotating screw into the extrusion head. However, it has not been possible heretofore to extrude aluminum commercially in a continuous manner, due to the properties of aluminum. When aluminum is in a molten condition, it attacks other metals with which it is contacted, and this action occurs to such an extent that the extruding machine would have too short a useful life for practical purposes. On the other hand, it would be highly advantageous to substitute aluminum for lead in the manufacture of cable sheathing, if it were possible to extrude the aluminum continuously in a practical manner.

According to the invention, the aluminum is first melted in an oven and atomized while in molten condition. The atomized aluminum is then solidified to form it into aluminum granules. Preferably, the molten aluminum is sprayed into a cooling liquid by a blast of steam, to form the granules, and the granules are separated from the cooling liquid in any suitable manner, as by centrifuging. The granulated aluminum is then subjected to a lubricating treatment by mixing it with oil, such as transformer oil, and is heated. The lubricating treatment is preferably effected concurrently with the heating step by feeding the granulated aluminum into a rotary oven and there spraying it with the oil. The lubricated and granulated aluminum, heated to a temperature considerably below its melting point, is then delivered to the extruding machine where, by reason of the preliminary processing previously described, it undergoes extrusion without attacking the metal parts which it contacts. It is important that the extruding operation be carried out quite promptly after the aluminum has been formed into the granules, that is, before any substantial oxidation of the granules has occurred. Otherwise, the aluminum will attack the metal of the extruding machine. Usually, the aluminum granules should be subjected to the extrusion operation within twenty-four hours after formation of the granules.

For a better understanding of the invention, reference may be had to the following detailed description of the preferred practice of the invention. This description refers to the accompanying drawing, in which the single illustration is a schematic view of a system for use in practicing the process.

Referring to the drawing, the aluminum is first melted in a refractory oven 1. The molten aluminum is poured from a spout 1a of the oven into an inclined trough 2, which delivers it into the path of a fluid jet issuing from a nozzle 3. The nozzle 3 is connected by a conduit 4 to a tank 5 where the fluid is maintained under pressure. Preferably, the tank 5 is a boiler for generating superheated steam, which is discharged through the nozzle 3 mm a;

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to form the jet. The steam may be maintained under a pressure of about 50 lbs/in. in the boiler 5 and discharged through nozzle 3 at a rate of about 10 parts of steam to one part of aluminum by volume. The molten aluminum discharging from the trough 2 is atomized by the steam jet or blast from nozzle 3 and sprayed by the jet into a body of water or other cooling liquid in a container 6. The finely divided aluminum is thus solidified in the cooling liquid to form granules.

Under the conditions described above with respect to the pressure of the steam jet and the relative volumes of steam and molten aluminum, the solidified particles of aluminum in the container 6 will be very small. They will be irregularly shaped but quite uniform in size, usually about .8 mm. in maximum diameter.

The granulated aluminum thus formed is withdrawn from the bottom of the container 6 through a valved pipe 6a and fed to a separator 8 for separating the granules from the cooling liquid. The separator 8 may be of any suitable type for separating solids from liquid but is preferably a centrifuge of the type which separates and discharges the solids continuously. The centrifuge is driven by a motor 8a.

From the centrifuge 8, the granulated aluminum passes into a rotary oven 10 by way of a stationary axial feed tube 10a. The granulated aluminum is heated in the oven it) to a temperature considerably below its melting point, usually a temperature between and 260 C. and preferably about C. At the same time, the granulated aluminum is lubricated by mixing it with transformer oil sprayed into the oven 10 through a stationary pipe 101) concentric with the pipe 18a. The oil is preferably introduced in an amount of about one part of oil to 1000 parts of aluminum by volume. The rotary motion of the oven 10 causes a thorough mixing of the oil with the granulated aluminum as it passes through the oven during the heating.

The granulated aluminum, heated and lubricated, is discharged from the lower end of the rotary oven 10 into a hopper 11 which feeds it into a casing 12 containing a rotating worm 13. The granules are forced by the worm 13 into the continuous extruder 14. As shown, the extruder includes a lower portion containing a vertical, rotating screw 14a which forces the granulated aluminum upwardly into the head or main portion 14b, where it is extruded under heavy pressure into the tubing or sheathing 15.

As previously stated, it is important that there be no substantial oxidation of the aluminum granules before the extruding operation is effected. When the granules are discharged from the oven 10, they are very susceptible to oxidation, since they are now at a temperature of about 180 C. or higher. However, it will be apparent from the drawing that the heated granules are enclosed by the casings for the conveyor screws 13 and 14a as the granules are fed under pressure by these screws to the extruding zone or head 14b. In other words, by thus excluding air from the heated granules, any substantial oxidation is avoided.

It will be understood that as a result of the treatment of the aluminum prior to the extruding, as previously described, the aluminum is fed to the continuous extruding operation in the form of substantially oxide-free granules. In this way, the continuous extruding machine 14 may be operated over a long period of time without being attacked or adversely affected by the aluminum. Moreover, the pulverizing of the aluminum, and the subsequent lubrication and heat treatment of the granules, have a beneficial effect upon the aluminum in making it better suited for the extruding operation.

I claim:

In the fabrication of aluminum cable sheathing, the

improvement which comprises atomizing the aluminum while in molten condition and solidifying the atomized aluminum to form it into granules, lubricating and heating the granules, the heating being to a temperature below the melting point of the aluminum, conveying the lubricated andheated granules continuously under pressure to ail-extruding zone while excluding air from the granules, and extruding the granules into the sheathing in said zone, the granulated aluminum being heated to a temperature of 180-260 C. prior to said conveying and extruding operations, the granulated aluminum being conveyed promptly from the heating operation to the extruding operation.

References Cited in the file of this patent UNITED STATES PATENTS Hoopes Oct. 8, 1907 

